"The NFL … was aware of the evidence and the risks associated with repetitive traumatic brain injuries virtually at the inception, but deliberately ignored and actively concealed the information from the plaintiffs and all others who participated in organized football at all levels," the plaintiffs claim.

U.S. District Judge Anita Brody is tasked with deciding whether the claims constitute a labor dispute, which according to the league's collective bargaining agreements would be settled by an arbitrator instead of a jury. The players argue the claims fall outside the agreements.

"Judge Brody has a tremendously difficult task in her hands, with billions of dollars at stake," said Paul Anderson, a Kansas City, Mo.-based attorney who founded NFLConcussionLitigation.com. "Her job is to follow the law, and law is, to an extent, a bit undecided so it could go either way."

An autopsy revealed Seau had signs of chronic traumatic encephalopathy, a brain disease tied to repetitive head trauma bearing similarities to Alzheimer's, Parkinson's and Lou Gehrig's disease as well as depression. Whether Belcher had CTE is unclear.

Of 85 athlete and veteran brains studied for signs of chronic traumatic encephalopathy at Boston University's Center for the Study of Traumatic Encephalopathy, 68 tested positive. Half belonged to former professional players.

But the NFL contends the research wasn't there when it formed the mild traumatic
brain injuries committee, led by a rheumatologist, which concluded in a 2005 study that "there were no adverse effects" associated with returning to the game after a concussion as long as the player was cleared by a knowledgeable team physician – results that were "in sharp contrast to the recommendations in published guidelines and the standard of practice of most college and high school football team physicians," according to the study.

The players claim research linking blows to the head with neurological problems dates back to 1928, and say that by publishing data to the contrary, the NFL "produced industry-funded, biased, and falsified research" and "actively sought to suppress the findings of other members of the medical communities" with contradictory results.

"The players' lawyers are going to try to find out exactly what the NFL knew, when they knew it, and how they acted on the information," said Anderson. But they can only do so if Judge Brody allows the cases to go to trial, opening the door for "far-reaching discovery," according to Anderson.

Fate of Concussion Lawsuits Lies With Judge

Anderson said it's impossible to predict Judge Brody's response, which could take months after today's hearing and will surely be appealed either way.

"She could grant the league's motion to dismiss, or deny it, or split it apart in various ways," said Anderson, explaining that the negligence claims could be dismissed and the fraud claims allowed to survive. "She could also rule in cases where there was no collective bargaining agreement in place."

The first collective bargaining agreement began in 1968, and there was no agreement in place between 1988 and 1993, according to Anderson.

If the lawsuits are allowed to go to trial, the NFL could be on the hook for the long-term medical care of its players, as well as damages that could rise into the billions, Anderson said.

"Juries in general are much more sympathetic to injured players and former heroes, and there's no limit on how much they could provide in damages," he said. "But if the NFL is able to get the cases in front of an arbitrator whose sole job is to interpret the contracts, they'll most likely rule in favor of the league."